Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$137.46	13.681%	$156.2659	$156.27	$156.25	$156.30
Purchase #2	$61.81	9.676%	$67.7907	$67.79	$67.80	$67.80
Purchase #3	$248.39	11.319%	$276.5053	$276.51	$276.50	$276.50
Purchase #4	$129.33	6.326%	$137.5114	$137.51	$137.50	$137.50
Purchase #5	$74.65	5.147%	$78.4922	$78.49	$78.50	$78.50
Purchase #6	$154.80	6.319%	$164.5818	$164.58	$164.60	$164.60
Purchase #7	$157.55	11.134%	$175.0916	$175.09	$175.10	$175.10
7 purchase totals =	$963.99		$1,056.2389	$1,056.24	$1,056.25	$1,056.30